Download Science 7 - 5.1 Notes

5.1 Minerals
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Rock is made up of one or more pure, naturally occurring, non-living
crystalline materials called minerals.
Most minerals are quite rare. Only a few, such as quartz, feldspar, andmica,
are found throughout Earth’s crust (the thin outermost layer of Earth).
A mineral can be an element (a pure substance) or a compound (two or
more elements combined).
The Mohs hardness scale
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A substances "Scratchability" can help to identify different rocks and
minerals
The Mohs hardness scale is a scale of ten minerals with a “hardness” value of
1 to 10
Talc is the "softest" mineral and Diamond is the "hardest" mineral
Crystals
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There are over 3000 minerals. Other properties, such as crystal formation,
help to identify them.
Crystals are the building blocks of minerals. Crystals occur naturally and
have straight edges, flat sides, and regular angles.
Most of the minerals in Earth’s crust grow into beautiful shapes according to
the six different crystal systems
Lustre
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Some minerals, such as gold and other metals, appear shiny —another clue to
their identity. Others, such as talc, can appear dull.
The “shini-ness,” or lustre, of a mineral depends on how light is reflected
from its surface. The surface of a mineral can reflect light in many different
ways.
If a mineral shines like a polished metal surface, it is said to have a metallic
lustre. If a mineral has a duller shine, it has a non-metallic lustre.
Color
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The colour of a mineral can also be a clue to its identity.
As in the case of gold and pyrite, however, color alone cannot identify a
mineral
In addition, not all minerals are the same colour all the time. For example, the
mineral corundum (made of aluminum and oxygen) is white when pure.
However, when it contains iron and/or titanium, it is blue (and is called a
sapphire). When it contains chromium, it is red (and is called a ruby).
Streak
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Streak is the color of the powdered form of the mineral.
Look-alikes, such as gold and pyrite, can be distinguished using a streak test.
Gold leaves a gold streak, while pyrite has a greenish-black or brown- black
streak.
Minerals with a greater hardness than the porcelain tile (hardness value of 7)
will not leave a streak.
Cleavage and Fracture
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The way a mineral breaks apart can be a clue to its identity. If it breaks along
smooth, flat surfaces, or planes, it is said to have cleavage.
Not all minerals have cleavage. Minerals that break with rough or jagged
edges have fracture